Check ebay for a 3" 3 spoke rear rim. I found one at a good price not long ago (under $50) The Y spoke rim at 2.75" may cause a 150 to have more of a rounded shape. However, if you can fit it on and you're ok with it, then go for it.
FWIW I'm not a purist, but for the sake of accuracy , the "Snowflake" rim is actually the rim for the R80 through R100 airheads. They are a cast wheel and are prone to cracking. As in catastrophic failure type cracking. The Y spoke on the K's doesn't have the same issue.